Within the field of oilwell production and drilling, a series of adapters and techniques have been developed to permit the placement of apparatus in a positively locked in position within the oilwell bore hole. Since some of the apparatus so positioned is designed to resist extreme back pressures and other anomalous conditions, a positive mechanical connection is required between the supporting lock and the oilwell borehole casing.
Initial locks of this nature were mechanically actuated. They function by expanding a plurality of locking dogs or latches into a mating groove or landing nipple firmly set within the overall well casing. The primary force these mechanical locks must resist is a sudden upward force induced by a blowout or a kick from deep within the well. The locking dogs are formed having essentially flat upper surface designed to engage with a flat annular region within the landing nipple, providing positive locking and engaging for mechanical linking of the lock to the landing nipple.
Since it is necessary, in practical use, that a lock be lowerable past a series of landing nipples until a desired location is reached downhole, the lower ends of the locking dogs have been beveled to permit them to pass, in sequence, a series of landing nipples. The lock is therefore set by lowering it past the desired landing nipple and then raising the drillstring until the lock positively engages. The accurate placement of such a lock has proven to be a problem and the subsequent removal of the lock is not always feasible.
As a result of the difficulty of accurately locating the desired landing nipple downhole, a series of magnetically coded and actuated lock mechanisms have been developed. These mechanisms code the landing nipples by stacking a series of permanently magnetized rings above the landing nipple. The rings are oriented in an arbitrary sequence of magnetic poles, so as to provide a particular magnetic pattern immediately above the nipple, identifying each individual landing nipple by the uniqueness of the pattern formed. A running tool supporting the lock to be lowered is then coded by providing a series of magnetic sensors chosen to match the magnetic pattern of the desired nipple. The running tool and the lock are lowered in a drillstring past each of the landing nipples in turn until the landing nipple is reached where the coded magnetic pattern matches that of the running tool. The identity of the magnetic fields is sensed to trigger an electrically fired explosive charge, providing propulsive power to expand and set the locking dogs within the landing nipple.
Such a magnetically coded setting lock is extremely precise. However, the requirement for explosive actuation, the necessity for precise detection of the magnetic fields, loss of the magnetic coding with age, and certain other problems associated with the reliability and safe performance of the running tool, make it desirable to have a capability of mechanically running and setting a lock within a landing nipple designed for magnetic actuation.
The design of the magnetically set locks is such that the landing nipple locking grooves have bevels both on their top and their bottom sides. The prior art mechanical locks cannot be used in such an environment as an over pressure on the mechanical lock will cause the dogs to be cammed in by the beveled upper surface of the nipple groove overriding the mechanical lock, and whatever devices are affixed to it. Since the primary purpose of the downhole landing nipple and lock mechanism is to set pressure resistant structures such as BOPs (blow out preventers) and similar emergency closing valves, such a situation is obviously unacceptable. Thus, it is considered in the current art that mechanical locks and running tools are totally incompatible with a casing string or tubing string which is made up with magnetically coded landing nipples. Likewise, a magnetically set locking mechanism cannot be utilized in a mechanically oriented casing and nipple string inasmuch as there are no magnetic segments to provide the locating signals necessary to activate a magnetically coded running tool and lock.